In our project, we look at sediment transport and deposition in a lowland river and on the adjacent floodplain, which means most of the work happens during and after flood events in winter and spring. On this, I have written several blog posts (Ecohydrology and MSc work in 2012; Ecosystem services of sedimentation; Unexpected early flooding in January and a second flood peak in April). However, what is the use of characterizing sediment and attached nutrient input is you have nothing to relate it too? During dry phases, the imported nutrients are made available for plant growth. This was the topic of my summer field campaign beginning of August and hence the rationale behind the title as now I completed the Four Seasons of Olszowa Droga, one of my sampling locations.

Autumn, winter, spring and summer in Olszowa Droga (Alder Road).

With vegetation productivity (measured as aboveground biomass of living vascular plants) and plant species recordings at every site where sediment transport and deposition was measured, we can now hopefully say something about the actual effect of sediment on vegetation productivity and plant species diversity.

Just as I was teaching my first year students, spring atmospheric conditions can vary dramatically over the years and especially the moment of spring thaw varies a lot in continental Poland. Some years, only by April did temperatures rose above 0 degrees and flooding started, while other years, already in January the spring-thaw flood was well underway. This year was one of the latter, so we expected water levels to have receded by April to facilitate collecting some of the sediment-trapping mats we placed on the floodplain.

But I did not start this blog for no reason with my lesson to the first year students. By the end of March, a rain period initiated a second flood period and our grass mats and Phillips samplers were submerged again. We still went to the field, because particularly the transport of sediment in the river is very interesting during such a second rain-flood peak (compared to the first snowmelt-flood). For the grass mats on the floodplain, all we did was checking if they were not trampled by elk or turned upside-down by a tractor. This gave me ample time to take some pictures. In May, we will return to finish the job!

I think we should honor the ecosystem services of natural wetland systems more. One of the ecosystem services we want to get a grip on is the natural nutrient retention function of floodplains. Mostly, nutrients in flood water are only measured as dissolved fraction. However, a substantial part of the nutrients is transported as particulate nutrients (organic matter) or bound to suspended sediment and this is what we study.

We use the natural Biebrza river valley (Poland) with annual snow-melt spring flood as study area. It has a fairly undisturbed character and there is a wealth of data available on surface and groundwater hydrology and vegetation.

April 2014: A promising reconnaissance surveyLast year during the spring flood we tested our new equipment: the Phillips sampler. Water flows through a small inlet tube and into a larger PVC cylinder. There, flow velocity drops and suspended sediment (with nutrients attached) is deposited. At the end, water exits the samplers through another small tube. The sediment can be collected and show cumulative suspended particulate nutrient transport over the period of submergence. To actually know how much is deposited on the floodplain, we installed artificial grass mats. Both techniques showed promising results so last October we up-scaled our experiment to more locations and higher spatial and temporal resolution.

If you are familiar with the water droplets on the green leaves or flower petals, have you seen or imaged when you put a droplet on the soil surface? Sometimes, the droplets do not immediately infiltrate into the soils, instead of that, they can stay several seconds, minutes even hours. This phenomenon is called ‘soil water repellency’ (SWR). Why is it worth doing research on this topic? The reason is that soil water repellency interrupts the water penetration, impacts the water uptake of plants and becomes a potential factor causing soil erosion. The hydrophobic soil organic matters derived from vegetation or microorganisms cause soil water repellency, we defined such components as ‘SWR-markers’. What are those SWR-markers and where do they come from?

Last week, the first year students of the Bachelor study Environmental Sciences went to the island Tiengemeten to do fieldwork. Most of Tiengemeten used to be farmland, however, after the last farmer left the island in 2007 nature has been developing rapidly. The students monitor this development by studying the flora and fauna, the soils, gas emissions from soils and the hydrology.

In our research project we look at how plants can work together to survive in very stressful environments. Much empirical work already showed that plants can facilitate each other’s survival in grazed or very dry environments. Big shrubs can for example protect young plants against grazers, thereby increasing survival of young plants. Also, big shrubs might provide shade to decrease drought stress for young neighbouring saplings. In my PhD project we look at how facilitation between plants might disappear when both grazing stress and drought stress become very severe. We expect that with increasing stress facilitation firstly becomes more important, but that at very high stress positive interaction will disappear again. Pinpointing the stress level at which facilitation wanes is crucial to better understand future land degradation in arid ecosystems.

Blog entry by Floris Keizer - Junior Lecturer / ResearcherThe marriage between the Environmental Sciences group of Utrecht University and one of the last undisturbed river floodplains in Central Europe has been a long one. Since the late 80’s, researchers from our group have visited the river floodplains and peatlands and brought it to the attention of the scientific community. The Biebrza valley in North-Eastern Poland is one of the last extensive undrained valley mires in Central Europe. The natural character of the valley peatlands is reflected in a very regular pattern of peat-forming plant communities (fig. 1).

Fig. 1. The Biebrza River with clearly visible pattern of different vegetation types perpendicular to the river. (source: Google Maps).